The present invention relates to ink jet printers. In particular, the invention relates to an apparatus and method for ink jet printing using ink jets that are subdivided into groups.
Ink jet printers are well known. A typical ink jet printer has a disposable ink cartridge containing an ink reservoir and a printhead. The printhead is fabricated from silicon and is formed to contain an array of thermally-actuated ink expulsion devices, also referred to herein as xe2x80x9cink energizing elements.xe2x80x9d The ink expulsion devices propel ink onto paper or other print media through small-diameter orifices referred to as xe2x80x9cnozzlesxe2x80x9d by electrically heating a water-based ink to its vaporization temperature.
One problem with ink jet printer and the print heads used in them, (due to the small-diameter orifices through which ink is ejected) is the tendency of the print head orifices to clog from either dried ink or dirt. Another problem is electrical failure. A commonly-observed artifact of one or more clogged or malfunctioning print head elements (clogged orifices or inoperative electronics) is the striation of printed output, i.e., streaks of lighter color or white that appear across printed areas, which is caused by an inoperative print element. Because there is no practical way to unclog an orifice or repair an ink ejector, replacing the entire cartridge is the only way to cure printed output defects.
Ink cartridge replacement to correct streaked print output is not a cost effective way to maintain print output quality, especially when the ink cartridge retains useable ink. One way to mitigate the effect of an ink jet print head nozzle blockage is to fabricate the print head with redundant print elements. In such a device, the effects of a failure of one print element might be reduced if a redundant print element is able to compensate for the failed element.
A problem with redundant print elements is the speed at which print data must be clocked into them. It is well-known that as the number of print elements increases, print data must be clocked into them at correspondingly higher rates, if overall printer speed (typically measured in printed xe2x80x9cpages per minutexe2x80x9d) is to be maintained. As print data clock rates into a print head increase, electromagnetic signals (noise) that such signals generate, and conversely are susceptible to, becomes problematic. Accordingly, there is a need for an apparatus and method that more efficiently addresses the problem of nozzle blockage and in particular, the need to rapidly xe2x80x9cclockxe2x80x9d print data into a print head having multiple redundant printing elements without generating electromagnetic interference.
Ink jet print head ink (or other fluid) energizing elements (including the circuitry used to pump electrical current through a heater resister as well as the heater resistor, a fluid chamber in the print head and orifices formed in the ink jet print head top plate) are logically arranged into ink jet clusters or groups. Print data from a host system is serially clocked into a shift register, the output bits of which are coupled to parallel-connected fluid expulsion elements that are individually controlled. The ink energizing elements of a group or cluster are fired sequentially using the same print data bit from the shift register so that each bit of print data is fired from multiple fluid expulsion elements, providing a redundant ink firing.